Gas discharge tube with magnetic means for extinguishing the discharge



t a i July 7, 1970 GQWAR ET AL 3 ,519,882

GAS DISCHARGE TUBE WITH MAGNETIC, MEANS FOR EXTINGUISHING THE DISCHARGE"Filed Oct. 25, 1968 2 Shets-Sheet' 1 l IIII 2Z\ 49 46 2g 2s- 1 5\: %?)47@g 4 24 i' 2s 9 10 i8 5?; H l7 I: i2 q7 N 28 l8 8 F 8 I fl :1 W I I I I,V l Fig.1 1 v Q INVENTORS JOHN eowm KENNETH GEORGE COOK BY@M y FiledOct. 25, 1968 July 7, 1970 I J. GOWAR ETAL GA S DISCHARGE TUBE WITHMAGNETIC MEANS FOR EXTINGUISHING THE DISCHARGE Load 2 Sheets-Sheet 2Pulse Generaror INVENTORS J'OHN GIOWAR KENNETHEEORQE C OK United StatesPatent GAS DISCHARGE TUBE WITH MAGNETIC MEANS FOR EXTINGUISHING THEDISCHARGE John Gowar, Rickmansworth, and Kenneth George Cook, Northwood,England, assignors to The M-O Valve Company Limited, London, England, aBritish company Filed Oct. 25, 1968, Ser. No. 770,520

Claims priority, application Great Britain, Nov. 3, 1967,

Int. Cl. H01j17/14, 17/56 US. Cl. 315-340 11 Claims ABSTRACT OF THEDISCLOSURE A gas-filled device having an anode, a cathode and a battlestructure, and means for producing a magnetic field. In the absence ofthe magnetic field a discharge may pass between the cathode and anode,but when the field is applied electrons emitted from the cathode areconstrained by the magnetic field to follow paths obstructed by thebaffle structure.

This invention relates to electric circuit interrupting devices.

Known electric circuit interruping devices operate relatively slowly andare therefore not suitable in applications where rapid operation isrequired, for example, for the protection of radio frequency oscillatingvalves in the event of the occurrence of a flash arc in the valve.

One way of overcoming this difficulty is to connect a so-called crow-bardevice, typically a gas discharge device, in parallel with the device tobe protected, which by-passes overload current around the device beingprotected until an associated interrupting device has had time tooperate. However, this method has the disadvantage that the magnitude ofthe current to be by-passed may be very high, and where there areseveral devices to be protected operating from a common power supply,has the disadvantage that failure of one device results in all the otherdevices being by-passed as well.

Thus there is a need for an electric circuit interrupting device capableof operating at a higher speed than known devices, and it is an objectof the present invention to provide such a device.

According to the present invention an electric circuit interruptingdevice includes an envelope containing a gas filling; an anode and acathode housed Within the envelope; a battle disposed within theenvelope between the anode and the cathode and allowing the passage of adischarge between the anode and the cathode; and means for producing amagnetic field whose lines of force extend Within the envelope in theregion of and in the direction of the path of said discharge, thearrangement being such that with the magnetic field applied electronsemitted from the cathode are constrained to follow paths obstructed bythe battle, thereby preventing the passage of a discharge between theanode and the cathode.

In the present specification the term gas filling is intended to includevapour filling.

-In a preferred arrangement in accordance with the invention the devicefurther includes a grid electrode disposed between the anode and thebafile, adjacent the anode, which, when maintained at a negativepotential with respect to the anode, allows the anode to be raised to ahigher positive potential with respect to the cathode before a dischargebetween the anode and cathode occurs than would be the case in theabsence of the grid electrode. With such an arrangement the gridelectrode may cnveniently be utilsed to trigger a discharge between theanode and the cathode.

One circuit interrupting device in accordance with the invention willnow be described by way of example, with reference to the accompanyingdrawing in which:

FIG. 1 is a sectional view of the device; and

FIG. 2 is a circuit diagram of a switching arrangement utilising thedevice shown in FIG. 1.

Referring to FIG. 1, the device has a generally cylindrical sealed glassenvelope 1 containing a filling of hydrogen at a pressure of about 0.2torr.

The envelope 1 houses an electrode structure including an anode 2, agrid 3, a cathode 4 and a bafile structure '5.

The cathode 4 is mounted on a metal base plate 6 which is disposed in aplane perpendicular to the axis of the envelope 1, near one end of theenvelope 1. The base plate 6 is supported on six metal rods 7 which aresealed through the adjacent end of the envelope 1 and at their innerends are sealed into tubular insulators 8 secured through the base plate6. The cathode 4 of conventional form and comprised a hollow cylindricalimpregnated body '9 which houses a spiral electrical resistance heater10 and is coaxially surrounded by a tubular heat shield 11 havinginwardly projecting fins 12 on its inner curved surface.

The anode 2 is in the form of a metal disc supported at one end of ametal rod 13 which is sealed through the end of the envelope 1 remotefrom the cathode 4, the rod 13 constituting a lead to the anode 2.

The grid 3 is in the form of a shallow circular cylindrical sheet metalbox, the anode being housed within thegrid box 3 with the two planarends 14 of the grid box 3 in parallel spaced relation with the anode 2,one on either side of the anode 2. The grid 3 is supported from atubular glass sleeve '15 which forms part of the envelope 1 andcoaxially surrounds parts of the rod 13.

In the planar end of the grid 3 nearer the cathode 4 there is formed anelongated rectangular slot 16, the axis of the envelope 1 passingthrough the centre of the slot 16.

The baffle structure 5 is made of mumetal sheet and is of hollowcircular cylindrical form. The structure 5 is supported coaxial with theenvelope 1, with one end closely adjacent the slotted end of the grid 3,by means of three metal rods 17 which extend perpendicularly between thecathode base plate 6 and the nearer end of the structure 5, the ends ofthe rods 17 being sealed into insulators 18 secured through the cathodebase plate 6 and the relevant end of the baffle structure 5.

In each end of the baffle structure 5 there is formed a circular recess'19 or 20, the recesses 19 and 20 being of the same depth and diameter.

In the side wall of the recess 19 there are formed eight equally spacedapart rectangular apertures 21, the lengths of the apertures 21 beingparallel to the axis of the envelope 1. This end of the baflle structure5 also carries a shallow, sheet metal cup-shaped member 22 having anaperture of somewhat larger diameter than the recess 13 formed in itsbase. The inner surface of the base of the member 22 is welded to theperiphery of the outer surface of the anode end of the baflle structure5, the side wall 23 of the member 22 extending towards the cathode 4withits outer surface close to the inner surface of the adjacent part ofthe envelope 1. The purpose of the member 22 is to assist in theprevention of unwanted long path breakdown in operation.

In the base of the recess 20 there is formed a circular aperture 24 andbetween this aperture 24 and the cathode 4 there is disposed a circularmetal plate 25 of slightly greater diameter than the aperture 24. Thisplate 25 is mounted from the adjacent end of the baffle structure 5 bymeans of metal brackets 26 so as to lie parallel to but spaced from thebase of the recess 20, in register with the aperture 24. The plate 25serves to inhibit contamination of the remainder of the electrodestructure with material evaporated from the cathode 4 in operation.

The baffle structure 5 houses a coil of wire 27 which coaxiallysurrounds the space between the bases of the recesses 19 and 20. Theends of the wire extend through apertures in the cathode end of thebaffie structure 5 and the cathode base plate 6 and are connected to twoof the rods 7 which serve as leads to the coil 27.

Others of the rods 7 serve as leads to the cathode heater 10.

The battle structure 5 and the grid 3 are provided with leads in theform of rods 28 and 29 :ealed through the side wall of the envelope 1.

In the absence of a current in the coil 27 the device operates in themanner of a conventional thyratron. With a suitable voltage appliedbetween the anode 2 and the cathode 4 a discharge between the anode 2and cathode 4 can be initiated by raising the grid 3 and the bafflestructure 5 to positive potentials with respect to the cathode 4.Thereafter the potentials of the grid 3 and the bafile structure 5 havelittle control of the discharge and the discharge can only beextinguished by reducing the anode-to-cathode voltage.

However, when a suitable current is applied to the coil 27, the passageof the discharge between the anode 2 and the cathode 4 is prevented dueto the electrons emitted by the cathode 4 being constrained to followthe lines of force of the magnetic field, produced by the current andtherefore to be obstructed by the anode end of the baffle structure 5.In addition, the ions produced within the baflle structure are alsoconstrained to follow the lines of force of the magentic field, and aretherefore obstructed by the cathode end of the baffle structure 5 andthe plate 25. As a result, insufficient ions are produced between thebaffle structure 5 and the grid 3 to support a discharge. Since thebalfie structure 5 is formed of mumetal, the magnetic field issubstantially contained within'the bafile structure 5 and therefore doesnot extend to the region of the anode 2 where its presence would lead tolong path breakdown.

One particular application of the device described above, by way ofexample, will now be described with reference to FIG. 2.

In this arrangement, the device 30 is connected in a circuit breakerarrangement for protecting a load 31 in the event of the load 31 drawingexcess current from a power supply (not shown).

The anode 2 of the device is connected via the load 31 and a paththrough a pulse generator 32 to the positive terminal 33 of the powersupply, the negative terminal 34 of the power supply being earthed. Thepulse generator 32 is arranged to produce a pulse in the event of thecurrent passing to the load 31 from the terminal 33 exceeding apredetermined value. This pulse is applied between the cathode and thegrid of a conventional hydrogen thyratron valve 35, the cathode of thethyratron 35 being earthed.

The anode of the thyratron 35 is connected via an inductor 36 and tworesistors 37 and 38 in series to a suitable positive potential withrespect to earth, and the junction between the resistors 37 and 38 isconnected via a capacitor 39 to one end of the coil 27 in the device 30.The other end of the coil 27 and the cathode 4 of the device 30 areearthed and the grid 3 and baffle structure -5 of the device areconnected via separate resistors 40 and 41 to one end of the secondarywinding 42 of a transformer 43, the other end of the winding 42 beingearthed.

In operation of the arrangement, after the power supply has been turnedon, the supply of current to the load 31 from the power supply isinitiated by the application of a pulse to the primary winding 44thereby momentarily driving the grid 3 positive with respect to thecathode 4 and causing a discharge to pass between the anode 2 and thecathode 4. In the event of the current passing through the load 31exceeding the predetermined value, the pulse produced by the generator32 initiates a discharge in the thyratron 35. As a result, the capacitor39 discharges via the coil 27, the anode-to-cathode path through thethyratron 35, the inductor 36 and the resistor 37, the discharge in thethyratron 35 extinguishing when the capacitor 39 has discharged. Theresulting pulse of magnetic field produced in the device 30 caused thedischarge in the device 30 to be extinguished so that current ceases tobe supplied to the load 31. The supply of current to the load 31 maysubsequently be re-established by the application of a further pulse tothe primary 44 of the transformer 43.

In one arrangement which has been used in practice, the voltage providedbetween the terminals 33 and 34 by the power supply is 7.5 kilovolts,and the pulse generator 32 is arranged to produce an output pulse whenthe current supplied to the load 31 exceeds 1 amp. The pulse supplied tothe coil 27 is such as to produce a pulse of magnetic field in the coil27 having a duration of 60 microseconds and a peak value of 1 kilogauss.

In alternative circuit breaker arrangements utilising switching devicesin accordance with the invention, the magnetic field producing means inthe switching device may be arranged to be energised by the currentpassing through the load protected by the circuit breaker arrangement,instead of by current derived from a separate power supply. With suchand arrangement the magnetic field produced in the switching device isarranged to attain a sufficiently high value to extinguish the dischargein the switching device only when the the current through the loadexceeds the maximum permissible value.

One particular application envisaged for circuit breaker arrangementsutilising devices in accordance with the invention is for protectingloads constituted by electric discharge devices, for example, radiofrequency oscillator valves.

We claim:

1. An electric circuit interrupting device including an envelopecontaining a gas filling; an anode and a cathode housed within theenvelope; a bafile disposed within the envelope between the anode andthe cathode and allowing the passage of a discharge between the anodeand the cathode; and means for producing a magnetic field whose lines offorce extend within the envelope in the region of and in the directionof the path of said discharge so as to constrain electrons emitted fromthe cathode to follow paths obstructed by the battle and thereby preventthe passage of a discharge between the anode and the cathode.

2. An electric circuit interrupting device as claimed in claim 1 whereinsaid baflle is of a material of high magnetic permeability.

3. An elelectric circuit interrupting device as claimed in claim 2wherein said baffle surround said means for producing a magnetic field.

4. An electric circuit interrupting device as claimed in claim 3 whereinsaid bafile is of hollow cylindrical form with at least one apertureformed in each end wall thereof.

5. An electric circuit interrupting device as claimed in claim 4 whereinthe end wall of the baffie nearer the anode has a recess formed therein,and the side wall of the recess has a plurality of apertures formedtherein.

6. An electric circuit interrupting device as claimed in claim 5 whereina plate of slightly greater dimensions than the aperture formed in theend wall of the bafile nearer the cathode is mounted parallel to butspaced from this end wall and in register with this aperture.

7. An electric circuit interrupting device as claimed in claim 1 whereina grid electrode is provided, disposed between the anode and the baflleand adjacent to the anode which, when maintained at a negative potentialwith respect to the anode, allows the anode to be raised to a higherpositive potential with respect to the cathode before a dischargebetween the anode and the cathode occurs than would be in the case inthe absence of the grid electrode.

8. An electric circuit interrupting device as claimed in claim 7 whereinthe grid electrode partially surrounds the anode.

9. An electric circuit interrupting device as claimed in claim 1 whereinthe means for applying a magnetic field comprise a coil.

10. On electric circuit interrupting device including an envelopecontaining a gas filling; an anode and a cathode housed within theenvelope; a 'bafile of hollow cylindrical form with at least oneaperture formed in each end wall thereof, disposed within the envelopebeween the anode and the cathode and allowing the passage of a dischargebetween the anode and the cathode; a grid electrode, disposed betweenthe anode and the bafile and adjacent to the anode which, maintained ata negative potential with respect to the anode, allows the anode to beraised to a higher positive potential with respect to the cathode beforea discharge between the anode and the cathode occurs than would be thecase in the absence of the grid electrode; and means, comprising a coilhoused within said baflle, for producing a magnetic field whose lines offorce extend within the envelope in the region of and in the directionof the path of said discharge so as to constrain electrons emitted fromthe cathode to follow paths obstructed by the baffie and 6 therebyprevent the passage of a. discharge between the anode and the cathode.

11. A circuit breaker arrangement for protecting a load, comprising anelectric circuit interrupting device as claimed in claim 1 connected inseries with the load and with a power supply; and means for controllingsaid means for producing a magnetic field to produce a pulse of themagnetic field in the event of the current passing to the load exceedinga predetermined value, which pulse is of suflicient magnitude toextinguish a discharge in the device.

References Cited UNITED STATES PATENTS 1,962,158 6/1934 Smith 313161 X2,217,186 10/1940 Smith 313l61 X 2,458,861 1/1949 Kohler 3l3161 X2,497,911 2/1950 Reilly et a1 3l3204 X 2,543,227 2/1951 Buckingham313-161 X 2,951,960 9/1960 Watrous 313204 X 3,435,287 3/1969 Jacobson313-161 X JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, AssistantExaminer US. Cl. X.R.

